The present invention relates to a printer, and a control unit and method for the printer.
In general, a printer receives print data from a host computer or the like, analyzes the received print data, and produces bit map data. The printer produces a visible image on a recording medium using the produced bit map data and outputs the image.
A typical printer of the above kind is a page printer (in particular, a laser printer) which is rapidly winning popularity these days. In general, when this kind of printer is used, a host computer that is an upper-level unit transmits print data described in dedicated page description language.
The printer therefore analyzes the received print data (composed of various commands), translates it into intermediate-language data, and produces bit map data using the intermediate-language data.
The pager printer is being adopted more widely because of the high speed and excellent quality of output images. In some printers, a large-capacity storage such as a hard disk is installed and used as a printer buffer in an effort to release an upper-level unit from a job of outputting print data.
A printer having a storage stores received print data in the form of a file and prints data that has been stored first (hereinafter, an action of storing received print data in the form of a file in a storage is referred to as “spooling,” and a resultant file is referred to as a “spool file”).
A general system (comprising a host computer and a printer) will be described in conjunction with a functional block diagram of FIG. 1.
In response to a print instruction (entered by an operator) through any kind of running application program, a host computer 101 translates print data 102, which is instructed to print, into printer language-written data compatible with a printer 105. After saving some printer language-written data in a spooler 103 (designed to translate data into printer language-written data), the host computer 101 transmits the data into the printer 105 via a communication channel 104.
Meanwhile, the printer spools received data in a spooler 106, and fetches data in the order in which the oldest spool file is fetched first. The fetched data is then analyzed by an emulator 107. A bit map is then expanded in a memory on the basis of the result of analysis. After bit map data concerning one page is expanded in the memory, the data is transferred to a  printer engine 108 according to a given procedure. Printing is then achieved.
When numerous spool files reside in the printer, time must be spent before printing of an intended spool file is started. The waiting time depends on the lengths of spool files printed before the printing of an intended spool file is started, and on the printing capability of the printer. This means that the waiting time depends on the processing capability of the printer. 
The processing capability of a printer will be discussed. Processing performed by a printer includes analyzing commands contained in print data, expanding print data into bit map data in a print buffer on the basis of the result of analysis, and printing print data according to the bit map data expanded in the print buffer. Above all, printing based on bit map data (for example, for a laser beam printer, bit map data is transferred as video signals in order to drive semiconductor laser elements, and a latent image is formed on a photosensitive drum, developed, and then transferred to a recording medium) is fixed due to mechanical restraints. If a printer permits fast command analysis and fast bit map expansion, the printer would prove very useful.